Sine wave generating circuit and test device

Abstract

To provide a sine wave generating circuit with improved distortion.SOLUTION: A first direct digital synthesizer 110 generates a digital sine wave fundamental signal DSIN1 having a frequency f0 in a normal operation mode and a calibration mode. A second direct digital synthesizer 120 generates a digital second harmonic correction signal DSIN2 having a frequency 2f0 in the normal operation mode. A correction circuit 130 superimposes a digital second harmonic correction signal DSIN2 on the digital sine wave fundamental signal DSIN1. A D / A converter 140 converts the output DSIN of the correction circuit 130 into an analog sine wave signal ASIN. An output buffer 150 receives an analog sine wave signal ASIN and outputs an analog sine wave output signal ASINOUT. An A / D converter converts the analog sine wave output signal into a digital signal in the calibration mode.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a sine wave generating circuit. [Background technology]

[0002] Analog sine wave signals (trigonometric functions) are used in various applications such as semiconductor test equipment, wireless communication circuits, etc. A known method for generating analog sine wave signals is to generate a digital sine wave signal using a Direct Digital Synthesizer (DDS) and convert the digital sine wave signal into an analog sine wave signal using a D / A converter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-166325 A

[0004] [overview] In this method, an active filter is inserted after the D / A converter to remove all components except the fundamental component of the sine wave from the output signal of the D / A converter. The distortion generated by this active filter reduces the accuracy of the final sine wave signal.

[0005] The present disclosure has been made in this context, and it is an exemplary purpose of an embodiment thereof to provide a sine wave generating circuit with improved distortion.

[0006] A sine wave generating circuit according to an embodiment of the present disclosure includes a first direct digital synthesizer that generates a digital sine wave fundamental signal of frequency f0 in a normal operation mode and a calibration mode; a second direct digital synthesizer that generates a digital second harmonic correction signal of frequency 2f0 in the normal operation mode; a correction circuit that superimposes the digital second harmonic correction signal on the digital sine wave fundamental signal; a D / A converter that converts an output of the correction circuit into an analog sine wave signal; an output buffer that receives the analog sine wave signal and outputs an analog sine wave output signal; an A / D converter that converts the analog sine wave output signal into a digital signal in the calibration mode; and a processing circuit that performs a fast Fourier transform on the digital signal output by the A / D converter to generate a spectrum in the calibration mode and sets parameters of the second direct digital synthesizer based on information on the frequency 2f0 of the spectrum.

[0007] Any combination of the above components, or mutual substitution of components or expressions between methods, devices, systems, etc., are also effective as aspects of the present invention or the present disclosure. Furthermore, the description in this section (Means for Solving the Problems) does not explain all essential features of the present invention, and therefore, subcombinations of the described features may also constitute the present invention. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram of a sine wave generating circuit according to an embodiment. [Diagram 2] FIG. 2 is a diagram for explaining the operation of the sine wave generating circuit of FIG. 1 in the calibration mode. [Diagram 3] FIG. 3 is a diagram for explaining the operation of the sine wave generating circuit of FIG. 1 in the normal operation mode. [Figure 4] FIG. 4 is a block diagram of a sine wave generating circuit according to an embodiment. [Diagram 5]FIG. 5 is a block diagram of the first and second direct digital synthesizers of FIG. [Figure 6] FIG. 6 is a diagram showing the measurement results of the sine wave generating circuit of FIG. [Figure 7] FIG. 7 compares the second harmonic of the spectrum before and after calibration. [Figure 8] FIG. 8 is a diagram showing the results of measurement of the sine wave generating circuit of FIG. 4 by an external measuring device. [Figure 9] FIG. 9 compares the second harmonic of the spectrum before and after calibration. [Figure 10] FIG. 10 is a block diagram of a sine wave generating circuit according to the first modification. [Figure 11] FIG. 11 is a block diagram of a test device according to an embodiment.

[0009] [Detailed Description] (Overview of the embodiment) A summary of some exemplary embodiments of the present disclosure will be described. This summary is intended to provide a simplified overview of some concepts of one or more embodiments for a basic understanding of the embodiments as a prelude to the detailed description that follows, and is not intended to limit the scope of the invention or disclosure. This summary is not intended to be an exhaustive overview of all possible embodiments, nor is it intended to identify key elements of all embodiments or to delineate the scope of some or all aspects. For convenience, the term "one embodiment" may be used to refer to one embodiment (example or variant) or multiple embodiments (examples or variants) disclosed in this specification.

[0010] A sine wave generating circuit according to one embodiment includes a first direct digital synthesizer that generates a digital sine wave fundamental signal of frequency f0 in a normal operation mode and a calibration mode; a second direct digital synthesizer that generates a digital second harmonic correction signal of frequency 2f0 in the normal operation mode; a correction circuit that superimposes the digital second harmonic correction signal on the digital sine wave fundamental signal; a D / A converter that converts an output of the correction circuit into an analog sine wave signal; an output buffer that receives the analog sine wave signal and outputs an analog sine wave output signal; an A / D converter that converts the analog sine wave output signal into a digital signal in the calibration mode; and a processing circuit that performs a fast Fourier transform on the digital signal output by the A / D converter in the calibration mode to generate a spectrum and sets parameters of the second direct digital synthesizer based on information on the frequency 2f0 of the spectrum.

[0011] In the calibration mode, the processing circuit detects second harmonics occurring due to distortion of the output buffer and determines the phase and amplitude of a digital second harmonic correction signal for canceling the second harmonic. In the normal operation mode, the digital second harmonic correction signal, the phase and amplitude of which are optimized by digital signal processing, is superimposed on the digital sine wave fundamental signal, thereby canceling the second harmonic occurring in the output buffer and reducing distortion of the finally obtained analog sine wave output signal.

[0012] In one embodiment, the processing circuit may perform a fast Fourier transform on the waveform data starting from a peak of the waveform of the digital signal generated by the A / D converter.

[0013] In one embodiment, the triangular wave generating circuit may further include a third direct digital synthesizer for generating a digital third harmonic correction signal having a frequency of 3f0 in the normal operation mode. The correction circuit may superimpose the digital second harmonic correction signal and the digital third harmonic correction signal on the digital sine wave fundamental signal. The processing circuit may set parameters of the third direct digital synthesizer based on information of the frequency 3f0 of the spectrum.

[0014] In one embodiment, the first and second direct digital synthesizers may have the same configuration and operate based on a common clock signal, which allows for more accurate correction.

[0015] In one embodiment, the first direct digital synthesizer may include a first accumulator that accumulates a first input value in response to a clock signal, and a first waveform generator that has a sine wave table and outputs a sine wave value corresponding to an output of the first accumulator by referring to the sine wave table. The second direct digital synthesizer may include a second accumulator that accumulates a second input value in response to a clock signal, and a second waveform generator that has a sine wave table and outputs a sine wave value corresponding to an output of the second accumulator. The second input value may be twice the first input value.

[0016] A test apparatus according to one embodiment includes a sine wave generating circuit that generates a sine wave signal to be supplied to a device under test that includes an A / D converter, and an analysis unit that analyzes a digital signal that the A / D converter outputs in response to the sine wave signal.

[0017] (Embodiment) Hereinafter, preferred embodiments will be described with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing will be given the same reference numerals, and duplicated descriptions will be omitted as appropriate. In addition, the embodiments are illustrative and do not limit the disclosure and invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the disclosure and invention.

[0018] In this specification, "a state in which component A is connected to component B" includes a case in which component A and component B are directly physically connected to each other, and a case in which component A and component B are indirectly connected to each other via other components that do not substantially affect the electrical connection state between them or that do not impair the function or effect achieved by their combination.

[0019] Similarly, "a state in which component C is provided between components A and B" includes not only the case in which components A and C, or components B and C, are directly connected to each other, but also the case in which they are indirectly connected to each other via other components that do not substantially affect the electrical connection between them or that do not impair the functions or effects achieved by their combination.

[0020] In addition, the vertical and horizontal axes of the waveform diagrams and time charts shown in this specification have been appropriately enlarged or reduced to facilitate understanding, and each waveform shown has been simplified to facilitate understanding.

[0021] 1 is a block diagram of a sine wave generating circuit 100 according to an embodiment of the present invention. The sine wave generating circuit 100 generates an analog sine wave output signal ASINOUT having a frequency f0.

[0022] The sine wave generating circuit 100 includes a first direct digital synthesizer 110, a second direct digital synthesizer 120, a correction circuit 130, a D / A converter 140, an output buffer 150, an A / D converter 160, and a processing circuit 170.

[0023] The sine wave generating circuit 100 can switch between a normal operation mode and a calibration mode. The sine wave generating circuit 100 operates in the calibration mode prior to the normal operation mode. For example, the sine wave generating circuit 100 may operate in the calibration mode every time the frequency f0 of the analog sine wave output signal ASINOUT is changed. Alternatively, the sine wave generating circuit 100 may operate in the calibration mode at predetermined time intervals, or may operate in the calibration mode triggered by a temperature change or the like.

[0024] The first direct digital synthesizer 110 generates a digital sinusoidal fundamental signal DSIN1 of frequency f0 in a normal operation mode and a calibration operation mode.

[0025] In the normal operating mode, the second direct digital synthesizer 120 generates a digital second harmonic correction signal DSIN2 having a frequency 2f0.

[0026] The correction circuit 130 superimposes the digital second harmonic correction signal DSIN2 on the digital sine wave fundamental signal DSIN1. In the normal operation mode, the output signal DSIN of the correction circuit 130 is a composite signal (sum signal or difference signal) of the digital sine wave fundamental signal DSIN1 and the digital second harmonic correction signal DSIN2. In the calibration mode, the digital second harmonic correction signal DSIN2 is not generated, so the output signal DSIN of the correction circuit 130 is DSIN1.

[0027] The D / A converter 140 converts the output signal DSIN of the correction circuit 130 into an analog sine wave signal ASIN.

[0028] The output buffer 150 has a filter characteristic, receives the analog sine wave signal ASIN, and outputs an analog sine wave output signal ASINOUT. In the output buffer 150, the output signal ASIN of the D / A converter 140 is amplified and unnecessary frequency components are removed. The gain of the output buffer 150 may be 1, may be greater than 1, or may be less than 1. The output buffer 150 may be a low-pass filter or a band-pass filter.

[0029] In the calibration mode, the A / D converter 160 converts the analog sine wave output signal ASINOUT into a digital signal DSINOUT.

[0030] In the calibration mode, the processing circuit 170 performs a fast Fourier transform (FFT) on the digital signal DSINOUT output by the A / D converter 160 to generate a complex spectrum. Then, based on information on the frequency 2f0 of the complex spectrum, the parameter PARAM of the second direct digital synthesizer 120 is set. Specifically, the parameter PARAM is set based on the amplitude information A 2f0 and the phase information φ 2f0 In a normal operation mode, the second direct digital synthesizer 120 may include the amplitude information A 2f0 and the phase information φ 2f0 A digital second harmonic correction signal DSIN2 is generated based on the

[0031] In FFT, a shift (delay) T on the time axis of a waveform in the time domain appears as a phase shift -Tω in the frequency domain. The processing circuit 170 may perform a fast Fourier transform on the waveform data starting from the peak of the waveform of the digital signal generated by the A / D converter 160. This ensures that the waveform is always cut out at the same position, eliminating the variation in phase information -Tω caused by the delay T.

[0032] The above is the configuration of the sine wave generating circuit 100. Next, the operation will be described.

[0033] Fig. 2 is a diagram for explaining the operation of the calibration mode of the sine wave generating circuit 100 of Fig. 1. On the left side of Fig. 2, the time waveform and amplitude spectrum of an analog or digital sine wave signal before the output buffer 150 are shown.

[0034] For ease of understanding and simplicity of explanation, it is assumed that the digital sine wave fundamental signal DSIN1 generated by the first direct digital synthesizer 110 is an ideal sine wave, and that waveform distortion in the correction circuit 130 and the D / A converter 140 can be ignored. In the calibration mode, the digital second harmonic correction signal DSIN2 is 0, so that the output signal DSIN of the correction circuit 130 is the same as the digital sine wave fundamental signal DSIN1 and is an ideal sine wave. The analog sine wave signal ASIN output from the D / A converter 140 is also an ideal sine wave. The amplitude spectrum of the sine wave signals DSIN1, DSIN, and ASIN contains only the fundamental wave f0 component, and the harmonic components 2f0, 3f0... can be ignored.

[0035] 2 shows the time waveform and amplitude spectrum of the analog or digital sine wave signals ASINOUT, DSINOUT downstream of the output buffer 150. Waveform distortion is introduced by the amplification of the analog sine wave signal ASIN by the output buffer 150, so that the amplified analog sine wave output signal ASINOUT contains high-order harmonic distortion components dist(2f0, 3f0, ...) in addition to the fundamental wave signal component sig(f0).

[0036] The complex spectrum of the output ASINOUT (DSINOUT) of the output buffer 150 is generated by FFT by the processing circuit 170, and the distortion component dist(2 f0 ) amplitude Ad 2f0 and phase φd 2f0 The processing circuit 170 adjusts the parameter PARAM of the second direct digital synthesizer 120, i.e., the amplitude A of the digital second harmonic correction signal DSIN2, so that the second harmonic 2f0 contained in the output ASINOUT of the output buffer 150 is cancelled. 2f0 and phase φ2f0 Determine.

[0037] The above is the operation of the calibration mode.

[0038] 3 is a diagram for explaining the operation of the sine wave generating circuit 100 of FIG. 1 in the normal operation mode. The left side of FIG. 3 shows the waveforms and amplitude spectra of the digital sine wave fundamental signal DSIN1 and the digital second harmonic correction signal DSIN2. The digital sine wave fundamental signal DSIN is the sum of the digital sine wave fundamental signal DSIN1 and the digital second harmonic correction signal DSIN2. The digital second harmonic correction signal DSIN2 has an amplitude A corresponding to the second harmonic distortion component dist(2f0) contained in the sine wave output signal ASINOUT (DSINOUT) measured in the calibration mode. 2f0 The digital second harmonic correction signal DSIN2 has a phase φ opposite to the phase of the second harmonic distortion component dist(2f0) contained in the sine wave output signal ASINOUT (DSINOUT) measured in the calibration mode. 2f0 has.

[0039] The digital sine wave fundamental signal DSIN is amplified by the output buffer 150. The amplified analog sine wave output signal ASINOUT can be decomposed into a component corresponding to the digital sine wave fundamental signal DSIN1 and a component corresponding to the digital second harmonic correction signal DSIN2. The component corresponding to the digital sine wave fundamental signal DSIN1 includes a signal component sig and a distortion component dist. This distortion component dist cancels out the component caused by the digital second harmonic correction signal DSIN2. Therefore, in the normal mode, the analog sine wave output signal ASINOUT generated by the sine wave generating circuit 100 is a low-distortion signal that contains almost no second harmonic components.

[0040] 4 is a block diagram of a sine wave generating circuit 100 according to an embodiment. The first direct digital synthesizer 110, the second direct digital synthesizer 120, and the correction circuit 130 can be implemented as a field programmable gate array (FPGA) 200. The processing circuit 170 is implemented as a microcontroller (MCU: Micro Controller Unit) 210.

[0041] The FPGA 200 also has a function of an interface between the A / D converter 160 and the processing circuit 170. That is, the FPGA 200 passes the digital sine wave output signal DSINOUT generated by the A / D converter 160 to the MCU 210 which is the processing circuit 170.

[0042] In one embodiment, a 16-bit, 50 Msps differential current output DAC (LT1668) manufactured by Analog Devices was used as the D / A converter 140. A 12-bit, 1 Msps ADC (BU79100) manufactured by Rohm was used as the A / D converter 160.

[0043] The output buffer 150 includes operational amplifiers Op1 and Op2, resistors, and capacitors. The upstream operational amplifier Op1 forms a low-pass filter together with the resistors and capacitors. The topology and order of the low-pass filter are not particularly limited. The downstream operational amplifier Op2 is a voltage follower and functions as a buffer.

[0044] Figure 5 is a block diagram of the first direct digital synthesizer 110 and the second direct digital synthesizer 120 of Figure 4. The first direct digital synthesizer 110 and the second direct digital synthesizer 120 have substantially the same configuration and are configured to operate based on a common clock signal CLK.

[0045] The first direct digital synthesizer 110 includes a first accumulator 112, a first waveform generator 114, and a multiplier 116. The first accumulator 112 accumulates a value Δt that defines the frequency of the digital sine wave fundamental signal DSIN1 in synchronization with the clock signal CLK. The frequency of the clock signal CLK is, for example, 50 MHz. The first accumulator 112 includes an adder 112a and a latch 112b. Each time the clock signal CLK is input, the adder 112a adds Δt to the value stored in the latch 112b, and stores the value after the addition in the latch 112b. The output value of the first accumulator 112 is phase information of the digital sine wave fundamental signal DSIN1, and the digital sine wave fundamental signal DSIN1 is calculated by: A1 sin(2πf0t+φ1) where φ1 is an initial phase corresponding to the initial value of latch 112b, and can be set to 0, for example.

[0046] The first waveform generator 114 includes an address decoder 114a and a waveform table 114b. The waveform table 114b stores data of a 1 / 4 cycle of a sine wave. The address decoder 114a refers to the waveform table 114b and outputs a sine wave value sin(2πf0t+φ1) corresponding to the phase information (2πf0t+φ1).

[0047] Multiplier 116 multiplies the output sin(2πf0t+φ1) of first waveform generator 114 by an amplitude A1 based on a gain parameter GAIN1.

[0048] Second direct digital synthesizer 120 is configured similarly to first direct digital synthesizer 110, and includes a second accumulator 122, a second waveform generator 124, and a second multiplier 126. The input value Δt×2 of second accumulator 122 is twice the input value Δt of first accumulator 112.

[0049] The output value of the second integrator 122 is phase information of the digital second harmonic correction signal DSIN2. A2 sin(2π 2f0t+φ2) where φ2 is the initial phase corresponding to the initial value of the latch 122b, and is set based on the phase parameter PHASE2.

[0050] The second waveform generator 124 outputs a sine wave value sin(4πf0t+φ2) corresponding to the phase information (4πf0t+φ2). This configuration ensures that the frequency of the digital second harmonic correction signal DSIN2 is exactly twice the frequency of the digital sinusoidal fundamental signal DSIN1.

[0051] A second multiplier 126 multiplies the output sin(4πf0t+φ2) of the second waveform generator 124 by an amplitude A2 based on a gain parameter GAIN2.

[0052] The gain parameter GAIN2 and the phase parameter PHASE of the second direct digital synthesizer 120 are parameter information PARAM set by the processing circuit 170. Specifically, the gain parameter GAIN2 is 2f0 The phase parameter PHASE2 is set based on the phase information φ 2f0 It is set based on.

[0053] Fig. 6 is a diagram showing the measurement results of the sine wave generating circuit 100 in Fig. 4. The upper part of Fig. 6 shows the amplitude spectrum of the digital sine wave output signal DSINOUT measured by the A / D converter 160 before calibration, i.e., in the calibration mode. Here, the frequency f0 of the fundamental wave is set to 100341.7969 Hz.

[0054] Distortion components appear in the second harmonic 2f0, the third harmonic 3f0, and the fourth harmonic 4f0, and their relative intensities to the fundamental wave f0 are -85.43 dB, -95.47 dB, and -99.38 dB, respectively.

[0055] The characteristics of the digital sine wave output signal DSINOUT before calibration were evaluated as follows. SNR(Signal to Noise Ratio) 71.76dB SINAD(Signal-to-Noise And Distortion Ratio) 71.55dB THD(Total Harmonic Distortion) -84.90dB SFDR(Spurious Free Dynamic Range) -85.43dB ENOB(Effective Number of Bits) 11.59Bit

[0056] The gain parameter GAIN2 is determined based on the strength of the second harmonic distortion component, which is -85.43 dB, and is set to -85.43 dB in this example. The phase of the second harmonic distortion component is measured to be -57.63°. Therefore, the inverted value of this, 57.63°, becomes the phase parameter PHASE of the second direct digital synthesizer 120.

[0057] 6 shows the amplitude spectrum of the digital sine wave output signal DSINOUT measured by the A / D converter 160 in the normal operation mode after calibration. The relative intensities of the distortion components of the second harmonic 2f0, the third harmonic 3f0, and the fourth harmonic 4f0 to the fundamental wave f0 after calibration are -96.48 dB, -96.10 dB, and -98.27 dB, respectively.

[0058] Figure 7 compares the second harmonic of the spectrum before and after calibration, where the second harmonic is buried in the noise floor and cannot be detected after calibration.

[0059] The characteristics of the digital sine wave output signal DSINOUT after calibration were evaluated as follows. SNR(Signal to Noise Ratio) 72.01dB SINAD(Signal-to-Noise And Distortion Ratio) 71.96dB THD(Total Harmonic Distortion) -96.10dB SFDR(Spurious Free Dynamic Range) -89.68dB ENOB(Effective Number of Bits) 11.66Bit

[0060] The evaluation results shown here are limited by the performance of the 12-bit, 1 Msps A / D converter 160. In order to evaluate the true performance of the sine wave generating circuit 100, an external measuring device was used to measure the analog sine wave output signal ASINOUT generated by the sine wave generating circuit 100. A 24-bit, 1 Msps digitizer (PXIe-4480) manufactured by National Instruments was used as the external measuring device.

[0061] Fig. 8 is a diagram showing the measurement results by an external measuring device of the sine wave generating circuit 100 of Fig. 4. The upper part of Fig. 8 shows the amplitude spectrum of the analog sine wave output signal ASINOUT measured by the external measuring device before calibration, i.e., in the calibration mode.

[0062] The relative intensities of the second harmonic 2f0, third harmonic 3f0, and fourth harmonic 4f0 distortion components to the fundamental wave f0 are -83.72 dB, -93.10 dB, and -103.93 dB, respectively.

[0063] The characteristics of the analog sine wave output signal ASINOUT before calibration were evaluated as follows. SNR(Signal to Noise Ratio) 86.85dB SINAD(Signal-to-Noise And Distortion Ratio) 81.64dB THD(Total Harmonic Distortion) -83.21dB SFDR(Spurious Free Dynamic Range) -83.72dB

[0064] The gain parameter GAIN2 is determined based on the strength of the second harmonic distortion component, which is -83.72 dB, and is set to -83.72 dB in this example. The phase of the second harmonic distortion component is measured to be -57.63°. Therefore, the inverted value of this, 57.63°, becomes the phase parameter PHASE of the second direct digital synthesizer 120.

[0065] The amplitude spectrum of the analog sine wave output signal ASINOUT measured by an external measuring device in normal operation mode after calibration is shown in the lower part of Fig. 8. The relative intensities of the distortion components of the second harmonic 2f0, the third harmonic 3f0, and the fourth harmonic 4f0 to the fundamental wave f0 after calibration are -92.90 dB, -93.34 dB, and -104.36 dB, respectively.

[0066] Figure 9 is a diagram comparing the second harmonic of the spectrum before and after calibration. After calibration, the intensity of the second harmonic is 9.2 dB smaller than before calibration.

[0067] The characteristics of the digital sine wave output signal DSINOUT after calibration were evaluated as follows. SNR(Signal to Noise Ratio) 87.32dB SINAD(Signal-to-Noise And Distortion Ratio) 85.43dB THD(Total Harmonic Distortion) -89.92dB SFDR(Spurious Free Dynamic Range) -92.90dB

[0068] The obtained SINAD of 85.43 dB exceeds the dynamic range (84.28 dB) of a 14-bit A / D converter. In other words, the analog sine wave output signal ASINOUT generated by the sine wave generating circuit 100 configured using the 12-bit A / D converter 160 can be used to evaluate the 14-bit A / D converter.

[0069] Next, a modification of the sine wave generating circuit 100 will be described.

[0070] (Variation 1) In the embodiment, the second harmonic is cancelled, but higher order harmonics may also be cancelled.

[0071] Fig. 10 is a block diagram of a sine wave generating circuit 100A according to the first modification. The sine wave generating circuit 100A includes a third direct digital synthesizer 180 in addition to the sine wave generating circuit 100 of Fig. 1. The third direct digital synthesizer 180 generates a digital third harmonic correction signal DSIN3 having a frequency of 3f0 in the normal operation mode. In the normal operation mode, the correction circuit 130A superimposes the digital second harmonic correction signal DSIN2 and the digital third harmonic correction signal DSIN3 on the digital sine wave fundamental signal DSIN1.

[0072] In the calibration mode, the processing circuit 170A performs FFT on the digital sine wave output signal DSINOUT output from the A / D converter 160 to generate a complex spectrum. Then, based on information on the frequency 3f0 of the spectrum, the parameter PARAM of the third direct digital synthesizer 180 is set. The parameter PARAM for the third direct digital synthesizer 180 is set based on the amplitude information A 3f0 and the phase information φ 3f0 In a normal operation mode, the second direct digital synthesizer 120 may include the amplitude information A 3f0 and the phase information φ 3f0 A digital third harmonic correction signal DSIN3 is generated based on the signal.

[0073] According to this modification, the second harmonic distortion can be cancelled by the digital second harmonic correction signal DSIN2, and the third harmonic distortion can be cancelled by the digital third harmonic correction signal DSIN3.

[0074] In the normal operating mode, a fourth direct digital synthesizer may be added to generate a digital fourth harmonic correction signal DSIN4 having a frequency of 4f0, to cancel fourth-order distortion components.

[0075] (Variation 2) In the embodiment, the second direct digital synthesizer 120 generates a digital second harmonic correction signal DSIN2 in antiphase with the second harmonic distortion component and adds it in the correction circuit 130, but the present disclosure is not limited to this. For example, the second direct digital synthesizer 120 may generate a digital second harmonic correction signal DSIN2 in phase with the second harmonic distortion component and subtract it in the correction circuit 130.

[0076] (Application) The following describes applications of the sine wave generating circuit 100. The sine wave generating circuit 100 can be used in a test apparatus for an A / D converter. FIG. 11 is a block diagram of a test apparatus 400 according to an embodiment. A device under test (DUT) 300 includes an A / D converter 302. The test apparatus 400 evaluates the A / D converter 302.

[0077] The test apparatus 400 includes the above-described sine wave generating circuit 100 and an analysis unit 410. The sine wave generating circuit 100 generates an analog sine wave output signal ASINOUT and supplies it to the A / D converter 302. The A / D converter 302 converts the analog sine wave output signal ASINOUT into a digital signal DUTOUT. The analysis unit 410 analyzes the output signal DUTOUT of the A / D converter 302 and evaluates the performance of the A / D converter 302. The analysis method by the analysis unit 410 is not particularly limited, but for example, the technology described in JP 2021-044690 A can be used.

[0078] (Additional Note) One aspect of the technology disclosed in this specification can be understood as follows.

[0079] (Item 1) a first direct digital synthesizer for generating a digital sinusoidal fundamental signal having a frequency f0 in a normal operation mode and in a calibration mode; a second direct digital synthesizer for generating, in the normal operating mode, a digital second harmonic correction signal having a frequency of 2f0; a correction circuit for superimposing the digital second harmonic correction signal on the digital sine wave fundamental signal; a D / A converter for converting an output of the correction circuit into an analog sine wave signal; an output buffer for receiving the analog sine wave signal and outputting an analog sine wave output signal; an A / D converter for converting the analog sine wave output signal into a digital signal in the calibration mode; a processing circuit that, in the calibration mode, performs a fast Fourier transform on the digital signal output by the A / D converter to generate a spectrum, and sets parameters of a second direct digital synthesizer based on information on a frequency 2f0 of the spectrum; A sine wave generating circuit comprising:

[0080] (Item 2) 2. The sine wave generating circuit according to item 1, wherein the processing circuit performs a fast Fourier transform on waveform data starting from a peak of the waveform of the digital signal generated by the A / D converter.

[0081] (Item 3) a third direct digital synthesizer configured to generate, in the normal operating mode, a digital third harmonic correction signal having a frequency of 3f0; the correction circuit superimposes the digital second harmonic correction signal and the digital third harmonic correction signal on the digital sine wave fundamental signal; 3. The sine wave generating circuit according to item 1 or 2, wherein the processing circuit sets parameters of the third direct digital synthesizer based on information of the frequency 3f0 of the spectrum.

[0082] (Item 4) 4. The sine wave generating circuit according to any one of items 1 to 3, wherein the first direct digital synthesizer and the second direct digital synthesizer have the same configuration and operate based on a common clock signal.

[0083] (Item 5) The first direct digital synthesizer a first integrator that integrates a first input value in response to the clock signal; a first waveform generator having a sine wave table, and outputting a sine wave value corresponding to the output of the first integrator by referring to the sine wave table; Including, The second direct digital synthesizer a second integrator that integrates a second input value in response to the clock signal; a second waveform generator having a sine wave table and outputting a sine wave value according to the output of the second integrator; 5. The sine wave generating circuit of item 4, comprising:

[0084] (Item 6) 6. A sine wave generating circuit according to any one of items 1 to 5, which generates the analog sine wave output signal to be supplied to a device under test having an A / D converter; an analysis unit that analyzes a digital signal output by the A / D converter in response to the analog sine wave output signal; A test apparatus for an A / D converter comprising: [Explanation of symbols]

[0085] 100 Sine wave generator circuit 110 First Direct Digital Synthesizer 112 First integrator 114 First Waveform Generator 116 First Multiplier 120 2nd Direct Digital Synthesizer 122 Second integrator 124 Second Waveform Generator 126 Second Multiplier 130 Correction circuit 140 D / A Converter 150 Output Buffers 160 A / D Converter 170 Processing circuit 180 3rd Direct Digital Synthesizer ASINOUT Analog sine wave output signal DSIN1 Digital sine wave fundamental signal DSIN2 Digital second harmonic correction signal DSIN3 Digital third harmonic correction signal 300 Devices Under Test 302 A / D Converter

Claims

1. In the normal operation mode and the calibration mode, the frequency f ０ a first direct digital synthesizer for generating a digital sinusoidal fundamental signal of In the normal operation mode, the frequency 2f ０ a second direct digital synthesizer for generating a digital second harmonic correction signal of a correction circuit for superimposing the digital second harmonic correction signal on the digital sine wave fundamental signal; a D / A converter for converting an output of the correction circuit into an analog sine wave signal; an output buffer for receiving the analog sine wave signal and outputting an analog sine wave output signal; an A / D converter for converting the analog sine wave output signal into a digital signal in the calibration mode; In the calibration mode, a spectrum is generated by performing a fast Fourier transform on the digital signal output by the A / D converter, and a frequency 2f of the spectrum is calculated. ０ a processing circuit for setting parameters of a second direct digital synthesizer based on the information of A sine wave generating circuit comprising:

2. 2. The sine wave generating circuit according to claim 1, wherein said processing circuit performs a fast Fourier transform on waveform data starting from a peak of the waveform of said digital signal generated by said A / D converter.

3. In the normal operation mode, the frequency 3f ０ a third direct digital synthesizer for generating a digital third harmonic correction signal of the correction circuit superimposes the digital second harmonic correction signal and the digital third harmonic correction signal on the digital sine wave fundamental signal; The processing circuitry detects the frequency 3f of the spectrum. ０ 3. The sine wave generating circuit according to claim 1, further comprising: a first input for inputting a first sine wave to said first direct digital synthesizer;

4. 3. The sine wave generating circuit according to claim 1, wherein said first direct digital synthesizer and said second direct digital synthesizer have the same configuration and operate based on a common clock signal.

5. The first direct digital synthesizer a first accumulator that accumulates a first input value in response to the clock signal; a first waveform generator having a sine wave table, and outputting a sine wave value corresponding to the output of the first integrator by referring to the sine wave table; Including, The second direct digital synthesizer a second integrator that integrates a second input value in response to the clock signal; a second waveform generator having a sine wave table and outputting a sine wave value corresponding to the output of the second integrator; 5. The sine wave generating circuit of claim 4, comprising:

6. a sine wave generating circuit as claimed in claim 1 or 2, which generates the analog sine wave output signal to be supplied to a device under test having an A / D converter; an analysis unit that analyzes a digital signal output by the A / D converter in response to the analog sine wave output signal; A test apparatus for an A / D converter comprising:

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